Collaborative Research: Exploring the Magmatic, Crustal, and Conduit Conditions Required for Mafic, Plinian Volcanism

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Low-silica 'mafic' magmas are the most common magmas to erupt on Earth. Because their viscosity is low, they usually form lava flows or weak explosive eruptions. However, mafic-composition volcanoes can produce much stronger, Plinian-style eruptions capable of dispersing ash fall over thousands of square kilometers, and producing deadly, landscape-altering ash flows that travel tens of kilometers from source. Despite their potential impact, the mechanisms responsible for generating mafic, Plinian eruptions are not understood. This project will benefit society by constraining the causes and consequences of such eruptions, which has global implications for the millions of people living at risk from mafic volcanic centers including the currently active Kilauea volcano in the USA. Two Boise State University (BSU) PhD students will be trained by the five participating scientists on the team, advancing discovery and understanding while promoting teaching, training, and learning. Undergraduate geoscience students from the Universidad de Concepcion (Chile) will be included in the field work and research, broadening participation of under-represented groups. The results and experience of the research team will be shared on the BSU magmatic and volcanic studies group Facebook page through a series of blog post and short videos of our field work that document the key elements of discovery associated with the project. Finally, the investigators and students will incorporate samples, stories, images and videos from the work in Chile into local and regional outreach efforts.This project targets the 13.4_ka (~12 km3 DRE) and ~12.6 ka (1 km3 DRE) mafic eruptions at Volcan Llaima, Chile, which produced extensive ash flow deposits found radially around the volcano. The difference in eruption sizes permits investigation of processes that promote large-volume, caldera forming mafic eruptions versus smaller volume Plinian mafic eruptions. A full suite of diverse but complimentary methods, including petrology, geochemistry, physical volcanology, decompression experiments, and rheology experiments, allows the research team to address the broad, fundamental research question of what magmatic and crustal conditions promote and trigger mafic, Plinian eruptions. More specifically, spatially and stratigraphically constrained petrologic and geochemical studies will allow us to investigate magmatic conditions during and prior to eruption, such as compositional variability of the magma and changes in chamber temperatures, pressures, and gas content. Establishing variability in these conditions will permit reconstruction of the magma plumbing system. A combination of all methods are used to constrain conduit conditions that promote high explosivity for mafic melts, including the interplay between ascent rate and degassing of the magma, as well as changes in magma rheology that prevent gas loss, promoting higher explosivity. The results of this work will have implications for understanding explosive mafic eruptive processes that extend to mafic centers worldwide, including both large-volume and small-volume mafic, Plinian eruptions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.